Abbreviations
    3G 3rd Generation    3GPP 3rd Generation Partnership Project    4G 4th Generation    ANDSF Access Network Discovery and Selection Function    AP Access Point    APN Access Point Name    CN Core Network    DSMIPv6 Dual Stack Mobile IP version 6    eNB enhanced Node B    EPC Evolved Packet Core    EPS Evolved Packet System    E-RAB E-UTRAN RAB    E-UTRAN Evolved UTRAN    GPRS General Packet Radio Service    GTP GPRS Tunneling Protocol    HESSID Homogeneous Extended Service Set Identification (IEEE 802.11u)    ID Identifier    IEEE Institute of Electrical and Electronics Engineers    IFOM IP flow mobility and seamless offload    IMS IP Multimedia Subsystem    IP Internet Protocol    LTE™ Long Term Evolution    MAPCON Multi Access PDN connectivity    MME Mobility Management Entity    NAS Non-Access Stratum    PDN Packet Data Network    PDU Protocol Data Unit    PGW PDN Gateway    QCI QoS Class identifier    QoS Quality of Service    RAB Radio Access Bearer    RAN Radio Access Network    RNC Radio Network Controller    RRC Radio Resource Control    S1AP S1 Application Protocol    SaMOG S2a Mobility over GTP    SGSN Serving GPRS Support Node    SGW Serving Gateway    SSID Service Set Identifier    TEID Tunnel Endpoint ID    UE User Equipment    UMTS Universal Mobile Telecommunication System    UTRAN UMTS RAN    WiFi™ synonymously used for WLAN    WLAN Wireless Local Area Network
WLAN/3GPP radio interworking is a 3GPP Study Item whose objective is described in RP-122038 (RAN Plenary #58, December 2012). 3GPP radio covers both LTE and UMTS (UTRAN).
Some operators want to integrate WLAN as an additional access network technology and also as backup of 3GPP cellular radio, and want to have tighter control over it. Operators want to utilize WLAN as much as possible when it is available while not pushing UEs to WLAN when WLAN is congested. Currently it is up to UE to select radio technology between WLAN and cellular, and operators can influence the selection via the policies in the ANDSF. However, some operators want to have more strict control of WLAN and cellular usage.
FIG. 1 shows an example architecture where WLAN offloading may be implemented. The UE on the left side is connected to both the 3GPP access network (UTRAN or LTE), and to WLAN. 3GPP Access network is connected via PGW of 3GPP Core network to an IP network (e.g. IP network 1). WLAN is connected via PGW to IP network 2. In addition, WLAN may be connected directly to some IP network. The IP networks may be different or the same, such as the Internet.
According to the current specifications, PDN connection based (also known as MAPCON) and flow based (also known as IFOM) mobility between 3GPP RAN and WLAN is supported, but flow based mobility is only supported when DSMIPv6 is (via S2c interface) is used as a mobility protocol. Over the S2c interface, the user plane is provided with related control and mobility support between UE and the PDN GW of the core network. Currently, no deployment using DSMIPv6 as mobility protocol is known and therefore, a RAN based solution for the control should preferably not be built on top of that.